The present invention relates to a method for preparing a drink by passing pressurised hot water in a sealed capsule, and to an apparatus and a capsule which allow this method to be implemented.
The present invention is intended in particular for preparing coffee, so, for the sake of simplicity, the following description refers explicitly only to that drink. However, the present invention shall still be considered as being intended for preparing any drink which can be obtained by passing hot water in a capsule containing a substance to be extracted or dissolved (normally grains or powder), according to the methods described below.
The use of disposable capsules for preparing coffee has been known for many years. They are usually sealed capsules, which may have filters, through which hot water, under pressure if necessary, is injected, to extract the coffee from the powder or grains contained in the capsule. The outflow of the drink is guaranteed by an opening made through the second wall of the capsule.
Since the quality of the drink obtained is very much dependent on the methods with which the water is passed through the capsule, with the passage of time many processes and apparatuses intended for preparing such drinks have been developed. For example, a capsule containing a mixture of powdered coffee can be used to obtain a simple infusion by slowly percolating low pressure hot water through it, or the so-called “espresso” (that is to say, a drink with significantly different organoleptic properties) if pressurised hot water is percolated through it. The quality of the espresso may be further improved by forced pre-infusion before starting to dispense the drink from the capsule, then maintaining a predetermined pressure in the capsule during the entire dispensing period.
Usually, the times, temperatures and pressures during the pre-infusion and dispensing steps, the intergranular flow speed and therefore the micro-turbulences generated are essential for obtaining a good organoleptic result. Since not all soluble substances contained in coffee are useful for an optimum result, attempts must be made to optimise the extraction cycle so that the appearance, smell and taste confirm the positive outcome of the process. Up to now, these empirical means have been the only ones considered really reliable to define the quality of the coffee.
Thus, the main technique for making a good quality espresso is broadly speaking widely known. However, in practice achieving a good level of quality and maintaining it constant with the passage of time are not certain and not easy. This is because there are many factors which contribute to the success of the operation, difficult to quantify and sometimes not even clearly identifiable, since even minimal changes in operating circumstances may produce considerably different effects. Moreover, when selecting production methods, preference should be given to simple, reliable methods with low industrial cost, but which guarantee a good end result. It is not commercially feasible to use methods that are too complex and therefore too expensive in order to achieve an optimum result.
As already indicated, one of the techniques recognised as being able to improve the result in terms of the quality of espresso coffee is pre-infusion. This consists of introducing hot water into the capsule, preventing it from flowing out until the internal pressure has reached a predetermined value (and if necessary this has been maintained for a predetermined time). This operation should allow the water to deeply penetrate the micro-pores of the coffee granules/powder, thanks to its own pressure compressing and therefore reducing the volume of the gaseous substances present in said pores. This deep penetration on one hand would allow the water to strike a significantly larger surface than that formed exclusively by the granule outer covering, and on the other would allow extraction of the aromas and essential oils found in the granule which represent most of those possessed by the coffee. Therefore, in this way, a significantly improved coffee flavour and aroma could be extracted.
The fact that preparing drinks using capsules has been a matter of great interest for a long time is indicated by the many patents relating to the subject. For example, the following:
CH 406561, CH 605293, DE 3722554, DE 7430109U, EP 199953, EP 211511, EP 242 556, EP 382001, EP 468078, EP 468079, EP 468080, EP 469162, EP 471094, EP 507905, FR 757358, FR 1198879, FR 1537031, FR 2062337, FR 2171306, FR 2556323, GB 938617, GB 2023086, U.S. Pat. No. 2,715,868, U.S. Pat. No. 2,899,886, U.S. Pat. No. 3,094,917, U.S. Pat. No. 3,292,527, U.S. Pat. No. 3,347,151, U.S. Pat. No. 3,403,617, U.S. Pat. No. 3,470,812, U.S. Pat. No. 3,589,272, U.S. Pat. No. 4,077,551, U.S. Pat. No. 4,136,202, U.S. Pat. No. 4,921,712 e WO 86/02537.
Further examples of patents describing various methods for opening the capsules are the following: WO 2005090196, EP 1557373, EP 1243210, EP 1674007, EP 0726053, EP 1599117, WO 9507648, U.S. Pat. No. 5,243,164, EP 1555218, EP 1247756.
Said patent documents substantially describe three main methods for preparing coffee or drinks using disposable sealed capsules: a first method in which the second wall of the capsule is pierced before water is injected into it, which therefore does not use pre-infusion; a second method making use of the inward opening of an openable portion of the base of the capsule (patents EP 1557373 and EP 1243210); and a third method, which instead uses pre-infusion, and in which the second wall of the capsule is pierced as a direct consequence of the increase in internal pressure due to injecting water into it.
Relative to the second method, patent EP 1243210 and patent EP 1557373 describe two very similar solutions in which the capsule opens by means of an inward deformation of an openable part of the base wall. In the case of patent EP 1557373, the openable part is obtained by pushing in the base wall along a weakening line using an external punch after the internal pressure has reached a predetermined value. In contrast, in the case of patent EP 1243210, the capsule is already made with the openable part, although the latter is shaped in such a way as to form a valve at the start of water injection into the capsule. In particular, the openable part rests on the remaining part of the base so that it cannot open outwards. Consequently, the base is actually opened by means of an outer contact element which interacts with the openable part when, following the increase in pressure, the capsule is sufficiently swollen.
In contrast, the third above-mentioned method has two main forms.
The first form, described for example in U.S. Pat. No. 4,136,202, involves the cartridge splitting open due to the increase in pressure, preferably at its weakened zones.
In the second form, coffee dispensing begins after the base of the capsule has been pierced due to the base swelling as a result of the internal pressure generated by the entry of the water, meaning that the base is torn against a fixed element which is integral with and projects from the base of the capsule housing body (patents EP 468 078 and EP 507 905). The tear obtained in this way allows the air and liquid to flow out at a pressure which depends on the resistance to piercing of the base of the capsule and the shape of the projecting sharp element.
However, these prior art technical solutions have several disadvantages.
When the base of the capsule is pushed in, a condition producing the above-mentioned compression of the air or gas in the coffee granule micro-pores has not been achieved. The increase in pressure occurs with the simultaneous presence of liquid and air/gas in the entire capsule and not just in the micro-pores, meaning that practically only the air outside the micro-pores is compressed. As a result, the water does not penetrate the micro-pores unless there are marginal phenomena such as micro-turbulences which can dynamically remove part of the air contained in some of these micro-pores.
However, it should be noticed that during the drink dispensing step, due to the dynamic resistance to drink outflow from the hole, there is a certain new increase in the capsule internal pressure, which can allow the water to partly penetrate the coffee granule micro-pores. On the other hand, following said new increase, in the absence of the reduction in pressure which would be necessary for the liquid penetrated to flow out, the solubilised substances only partly flow out of the granule.
Thus, the prior art, although allowing results in which the quality of the drink is sometimes good, implement substantially inefficient pre-infusion treatments, and therefore are susceptible of further, significant improvements. They are also not without construction problems, including in particular the narrowness of the components tolerances necessary to guarantee tearing of the base walls of the capsules in the required times and ways, with the necessary repeatability and constancy with the passage of time.
It is necessary to work very close to the maximum limits of capsule resistance to piercing in order to obtain satisfactory results, which makes it difficult to optimise the set of various parameters and tolerances involved (maximum pressure which can be reached by the pump, deformability of the capsule material and relative thickness, nature of the compound, ambient temperature, incisiveness of the piercing element, degree of projection of the latter and size tolerances in general).
From all of this it is possible to infer that there is a risk of early piercing or even no piercing at all. Moreover, perforation may sometimes be too resolute, leaving open a hole which does not sufficiently oppose the outflow, or the hole may have difficulty opening, lengthening the dispensing time more than necessary.
As already indicated, other known methods mechanically pierce the base of the capsule (in some cases removing portions, in others plastically deforming the edges delimiting the hole) before or simultaneously with the start of water entering the capsule. For simple construction, those methods do not use pre-infusion, instead seeking an acceptable result in other ways: high operating pressure values, very fine size of the grains ground, high operating temperatures, reduced hydraulic flow rates, turbulence phenomena induced by special capsule internal shapes. All of these methods are partly suitable for the purpose but are in turn complex and not very reliable (without unacceptable increases in production costs). Other methods use electronic control devices, obtaining a very moderate pre-infusion at atmospheric pressure and then raise the pressure during the subsequent step, increasing the pump capacity.
In short, all of these prior art methods obtain results which are uncertain or not entirely satisfactory, often with considerably high costs.
In this situation the technical purpose which forms the basis of the present invention is to provide a method for preparing a drink which overcomes the above-mentioned disadvantages, as well as providing an apparatus and a capsule which allow this method to be implemented.
In particular the technical purpose of the present invention is to provide a method for preparing a drink and a relative capsule and apparatus able to allow the preparation of drinks with optimum organoleptic properties.
Another technical purpose of the present invention is to provide a method for preparing a drink and a relative capsule and apparatus which guarantee a result which can be repeated and remains constant with the passage of time.
The technical purpose specified and the aims indicated are substantially achieved by a method for preparing a drink, the relative apparatus and capsule as described in the claims herein.